Figure 7. A schematic model summarizing the differential role of SP-A in modulating T cell activation and proliferation depending upon the strength of activating signal.

SP-A allows for low grade, basal levels of proliferation in part by maintaining [Ca²⁺]_i levels, and thus may help maintain the immune repertoire in T cells. Initial expansion in response to strong signals does occur in the presence of SP-A, but it acts as a brake to prevent runaway inflammation at later stages of strong T cell responses. Since extensive proliferation and differentiation to terminal effector cells that ultimately undergo activation induced cell death is avoided, the generation of multifunctional T cells that eventually form memory cells might be enhanced in the presence of SP-A.